Carrier (redirected from letter carrier)

(1) An organization that provides communications and networking services. A communications and networking "service provider." See common carrier and private carrier.

(2) A waveform that has a fixed center frequency. It is used to contain data and establish a unique channel that can be identified independently of other channels. Carriers are the primary method used to send wireless signals through the air in order to differentiate transmitting stations. For example, AM and FM radio, TV, satellite and Wi-Fi all use carriers. In fact, AM and FM radio actually use the carrier frequency as their station's channel number.

Multiple Carriers - Multiple Data Streams
Carriers are also used to transmit multiple channels simultaneously within a wire or fiber. For example, several voice, data and video signals can travel over the same line, each residing in its own carrier vibrating at a different frequency.

Multiple Carriers - One Data Stream
Instead of sending a separate stream of data in each carrier, multiple carriers can be used for only one channel of data. For example, the widely used orthogonal frequency division multiplexing (OFDM) method uses numerous carriers (subcarriers) for only one transmitting channel and one stream of data (see OFDM). See modulation and subcarrier.

Carrier Signal

The radio station transmits audio in a carrier, which is altered (modulated) with the analog signal. The receiving tuner latches onto the carrier's center frequency and isolates the audio, which is sent to the amplifier. The amplifier boosts the signal and sends it to the speakers. Carriers are also used to transmit digital data (see modulation).

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Carrier

A periodic waveform upon which an information-bearing signal is impressed. This process is known as modulation and comprises a variety of forms such as amplitude, phase, and frequency modulation. The most common type of carrier is the sinusoidal carrier, but any periodic waveform followed by a band-pass filter can serve as a carrier.